1. Field of the Invention
The invention relates to synthetic hydrocarbon oils and a method for their manufacture. More particularly, the invention is concerned with copolymers of propylene, higher 1-olefins and ethylene, wherein the ethylene in the final product is present in very small amounts.
2. Discussion of the Prior Art
Copolymerization of olefin mixtures using a Ziegler catalyst is known. These may, for example, include a catalyst made by combining a transition metal compound with a metal alkyl or an alkyl metal halide.
As the prior art knows, as taught, for example, in U.S. Pat. No. 2,923,919, in producing synthetic hydrocarbon lubricating oils, the attainment of high viscosity index is generally due to the presence in the overall oil of high molecular weight polymer ends. This same patent teaches that when the ethylene content falls below 29 mol % of ethylene in the oil, the combination of high pour point and low viscosity index will be unacceptable.
Other U.S. patents having similar disclosures are U.S. Pat. Nos. 3,676,521, 3,737,477 and 3,851,011.
None of these patents suggest that synthetic hydrocarbon oils having acceptable pour points and viscosity indexes can be made by copolymerizing propylene and ethylene when the finished oil has a very low content of ethylene.